Hydrodynamic Regime Research Articles

Diversity of Cryptofaunal Nematode Assemblages along the Jardines de La Reina Coral Reef, Southern Cuba

Cryptofaunal nematodes, those living on the hard substrate of the coral reefs, are largely unknown in terms of diversity and assemblage structure. We described nematode assemblages at seven sites spanning about 200 km along Jardines de La Reina, a well-preserved reef system in the Greater Antilles. We identified about 3000 nematodes, mostly of the families Desmodoridae and Chromadoridae; the most abundant species were Croconema cinctum, Desmodora communis, and Euchromadora vulgaris. The regional richness was moderate with 70 observed species (0.95 confidence interval: 65–75 species) and 75 extrapolated species (0.95 CI: 68–83 species). This richness was lower than in other reef biotopes, maybe reflecting evolutionary constraints due to interactions with stony corals. The local expected richness at 100 individuals was similar among sites, with a median of 26 species (0.95 CI: 20–34 species), and likely caused by diversification rate and evolutionary time acting at the same pace on populations. The taxonomic β-diversity was high and without differences among sites (median: 0.85; 0.95 CI: 0.33–1), probably due to significant substrate heterogeneity at 10-cm scale. The prevalence of replacement over richness difference suggests that local processes (e.g., environmental filtering and competition) contribute more to β-diversity than niche availability, which would be largely similar across the reef terraces. Contrary to our expectations, no gradient of assemblage structure occurred, nor significant effect of benthic cover on nematodes. However, nematode functional structure showed a conservative set of biological traits reflecting adaptations to hydrodynamic regime: armed oral cavity/intermediate colonizing capability/ornamented cuticles/conical tail. Our results provide insights about the taxonomic and functional diversity of nematodes and highlight the vast knowledge gaps about the processes ruling the meiofauna community structure in coral reefs.

Alternative routes to electron hydrodynamics

Viscous flow of interacting electrons in two dimensional materials features a bunch of exotic effects. A model resembling the Navier-Stokes equation for classical fluids accounts for them in the so called hydrodynamic regime. We perform a detailed analysis of the physical conditions to achieve electron hydrodynamic transport and find alternative routes: the application of a magnetic field or a high-frequency electric field in the absence of very frequent inelastic collisions. As a major conclusion, we show that the conventional requirement of frequent electron-electron collisions is too restrictive and, as a consequence, materials and phenomena to be described using hydrodynamics are widened. In view of our results, we discuss recent experimental evidence on viscous flow and point out alternative avenues to reduce electric dissipation in optimized devices.

Experimental investigation of micro-machining of borosilicate glass using an ultrasonic assisted rotary electrochemical discharge machining (UA-RECDM) process

Electrochemical discharge machining is an advanced micro-machining process for machining of conductive as well as non-conductive hard and brittle materials, e.g. glass, ceramics, silicon wafer, etc. The present work explores the machining of glass using an in-house developed novel ultrasonic assisted rotary electrochemical discharge machining setup. The setup has specialized features, such as using ultrasonic vibrations to tool the electrode and incorporating rotary motion for manipulating the workpiece. Experiments were conducted using a one factor at a time approach by varying the tool feed rate, the amplitude of the vibrations and the rotation of the workpiece as process parameters. The quality of the machining output was evaluated by observing two key parameters: the overcut and the circularity of the hole. It was observed that as the workpiece rotation speed increased from 40 rpm to 60 rpm, the overcut in the machined samples decreased from 181.378 μm to 163.564 μm. The rotary motion of the workpiece caused a seeping action of the electrolyte in the hydrodynamic regime, leading to the formation of a thin gas film and the stabilization of the discharging process. The morphology of the machined hole exhibits better circularity, low heat-affected zones, minimum micro-cracks and smooth edges at its periphery due to stable discharge formation.

Emergent gauge symmetry in active Brownian matter.

We investigate a two-dimensional system of interacting active Brownian particles. Using the Martin-Siggia-Rose-Janssen-de Dominicis formalism, we built up the generating functional for correlation functions. We study in detail the hydrodynamic regime with a constant density stationary state. Our findings reveal that, within a small density fluctuations regime, an emergent U(1) gauge symmetry arises, originated from the conservation of fluid vorticity. Consequently, the interaction between the orientational order parameter and density fluctuations can be cast into a gauge theory, where the concept of "electric charge density" aligns with the local vorticity of the original fluid. We study in detail the case of a microscopic local two-body interaction. We show that, upon integrating out the gauge fields, the stationary states of the rotational degrees of freedom satisfy a nonlocal Frank free energy for a nematic fluid. We give explicit expressions for the splay and bend elastic constants as a function of the Péclet number (Pe) and the diffusion interaction constant (k_{d}).

Eliminating the channel resistance in two-dimensional systems using viscous charge flow

Driven by the pursuit of high-performance electronic devices and the exploration of quantum phenomena, research into two-dimensional (2D) systems and materials, has unveiled their exceptional properties and potential applications. While extensive efforts have centered on minimizing contact resistance, reducing the intrinsic channel resistance within the conducting material remains a formidable challenge. Research in this direction has focused on investigating superconductivity and ballistic transport. However, the practical applications of these phenomena are usually constrained by the requirement for cryogenic conditions. Charge transport in the hydrodynamic regime emerges as a versatile alternative, offering enhanced resilience to these challenges, and making it a promising avenue for effectively reducing channel resistance in 2D systems. The current perspective delves into charge hydrodynamics, exploring its mechanisms, recent advancements, enduring challenges, and its potential in reducing the channel resistance.

Carrollian Fluids and Spontaneous Breaking of Boost Symmetry.

In the hydrodynamic regime, field theories typically have their boost symmetry spontaneously broken due to the presence of a thermal rest frame although the associated Goldstone field does not acquire independent dynamics. We show that this is not the case for Carrollian field theories where the boost Goldstone field plays a central role. This allows us to give a first-principles derivation of the equilibrium currents and dissipative effects of Carrollian fluids. We also demonstrate that the limit of vanishing speed of light of relativistic fluids is a special case of this class of Carrollian fluids. Our results shine light on the thermodynamic properties and thermal partition functions of Carrollian field theories.

A structure preserving numerical method for the ideal compressible MHD system

We introduce a novel structure-preserving method in order to approximate the compressible ideal Magnetohydrodynamics (MHD) equations. This technique addresses the MHD equations using a non-divergence formulation, where the contributions of the magnetic field to the momentum and total mechanical energy are treated as source terms. Our approach uses the Marchuk-Strang splitting technique and involves three distinct components: a compressible Euler solver, a source-system solver, and an update procedure for the total mechanical energy. The scheme allows for significant freedom on the choice of Euler's equation solver, while the magnetic field is discretized using a curl-conforming finite element space, yielding exact preservation of the involution constraints. We prove that the method preserves invariant domain properties, including positivity of density, positivity of internal energy, and the minimum principle of the specific entropy. If the scheme used to solve Euler's equation conserves total energy, then the resulting MHD scheme can be proven to preserve total energy. Similarly, if the scheme used to solve Euler's equation is entropy-stable, then the resulting MHD scheme is entropy stable as well. In our approach, the CFL condition does not depend on magnetosonic wave-speeds, but only on the usual maximum wavespeed from Euler's system. To validate the effectiveness of our method, we solve a variety of ideal MHD problems, showing that the method is capable of delivering second-order accuracy in space for smooth problems, while also offering unconditional robustness in the shock hydrodynamics regime as well.

Attractive carbon black dispersions: Structural and mechanical responses to shear

The rheological behavior of colloidal dispersions is of paramount importance in a wide range of applications, including construction materials, energy storage systems, and food industry products. These dispersions consistently exhibit non-Newtonian behaviors, a consequence of intricate interplays involving colloids morphology, volume fraction, and interparticle forces. Understanding how colloids structure under flow remains a challenge, particularly in the presence of attractive forces leading to cluster formation. In this study, we adopt a synergistic approach, combining rheology with ultra small-angle x-ray scattering, to probe the flow-induced structural transformations of attractive carbon black (CB) dispersions and their effects on the viscosity. Our key findings can be summarized as follows. First, testing different CB volume fractions, in the high shear rate hydrodynamic regime, CB particles aggregate to form fractal clusters. Their size conforms to a power law of the shear rate, ξc∝γ˙−m, with m≃0.5. Second, drawing insights from the fractal structure of clusters, we compute an effective volume fraction ϕeff and find that microstructural models adeptly account for the hydrodynamic stress contributions. We identify a critical shear rate γ∗˙ and a critical volume fraction ϕeff∗, at which the clusters percolate to form a dynamical network. Third, we show that the apparent yield stress measured at low shear rates inherits its properties from the percolation point. Finally, through data scaling and the integration of Einstein’s viscosity equation, we revisit and discuss the Caggioni–Trappe–Spicer model, revealing a significant connection between its empirical parameters and the structural properties of CB dispersions under flow.

Fluctuation-response relation as a probe of long-range correlations in nonequilibrium quantum and classical fluids.

The absence of a simple fluctuation-dissipation theorem is a major obstacle for studying systems that are not in thermodynamic equilibrium. We show that for a fluid in a nonequilibrium steady state characterized by a constant temperature gradient the commutator correlation functions are still related to response functions; however, the relation is to the bilinear response of products of two observables, rather than to a single linear response function as is the case in equilibrium. This modified fluctuation-response relation holds for both quantum and classical systems. It is both motivated and informed by the long-range correlations that exist in such a steady state and allows for probing them via response experiments. This is of particular interest in quantum fluids, where the direct observation of fluctuations by light scattering would be difficult. In classical fluids it is known that the coupling of the temperature gradient to the diffusive shear velocity leads to correlations of various observables, in particular temperature fluctuations, that do not decay as a function of distance, but rather extend over the entire system. We investigate the nature of these correlations in a fermionic quantum fluid and show that the crucial coupling between the temperature gradient and velocity fluctuations is the same as in the classical case. Accordingly, the nature of the long-ranged correlations in the hydrodynamic regime also is the same. However, as one enters the collisionless regime in the low-temperature limit the nature of the velocity fluctuations changes: they become ballistic rather than diffusive. As a result, correlations of the temperature and other observables are still singular in the long-wavelength limit, but the singularity is weaker than in the hydrodynamic regime.

Exploring Challenging Properties of Liquid Metallic Systems through Machine Learning: Liquid La and Li4Pb Systems.

In this machine learning (ML) study, we delved into the unique properties of liquid lanthanum and the Li4Pb alloy, revealing some unexpected features and also firmly establishing some of the debated characteristics. Leveraging interatomic potentials derived from ab initio calculations, our investigation achieved a level of precision comparable to first-principles methods while at the same time entering the hydrodynamic regime. We compared the structure factors and pair distribution functions to experimental data and unearthed distinctive collective excitations with intriguing features. Liquid lanthanum unveiled two transverse collective excitation branches, each closely tied to specific peaks in the velocity autocorrelation function spectrum. Furthermore, the analysis of the generalized specific heat ratio in the hydrodynamic regime investigated with the ML molecular dynamics simulations uncovered a peculiar behavior, impossible to discern with only ab initio simulations. Liquid Li4Pb, on the other hand, challenged existing claims by showcasing a rich array of branches in its longitudinal dispersion relation, including a high-frequency LiLi mode with a nonhydrodynamic optical character that maintains a finite value as q → 0. Additionally, we conducted an in-depth analysis of various transport coefficients, expanding our understanding of these liquid metallic systems. In summary, our ML approach yielded precise results, offering new and captivating insights into the structural and dynamic aspects of these materials.

On-chip fabrication and in-flow 3D-printing of microgel constructs: from chip to scaffold materials in one integral process

Bioprinting has evolved into a thriving technology for the fabrication of cell-laden scaffolds. Bioinks are the most critical component for bioprinting. Recently, microgels have been introduced as a very promising bioink, enabling cell protection and the control of the cellular microenvironment. However, the fabrication of the bioinks involves the microfluidic production of the microgels, with a subsequent multistep process to obtain the bioink, which so far has limited its application potential. Here we introduce a direct coupling of microfluidics and 3D-printing for the continuous microfluidic production of microgels with direct in-flow printing into stable scaffolds. The 3D-channel design of the microfluidic chip provides access to different hydrodynamic microdroplet formation regimes to cover a broad range of droplet and microgel diameters. After exiting a microtubing the produced microgels are hydrodynamically jammed into thin microgel filaments for direct 3D-printing into two- and three-dimensional scaffolds. The methodology enables the continuous on-chip encapsulation of cells into monodisperse microdroplets with subsequent in-flow cross-linking to produce cell-laden microgels. The method is demonstrated for different cross-linking methods and cell lines. This advancement will enable a direct coupling of microfluidics and 3D-bioprinting for scaffold fabrication.

Chaos and anomalous transport in a semiclassical Bose-Hubbard chain.

We study chaotic dynamics and anomalous transport in a Bose-Hubbard chain in the semiclassical regime (the limit when the number of particles goes to infinity). We find that the system has mixed phase space with both regular and chaotic dynamics, even for long chains with up to 100 wells. The consequence of the mixed phase space is strongly anomalous diffusion in the space of occupation numbers, with a discrete set of transport exponents. After very long times the system crosses over to the hydrodynamic regime with normal diffusion. Anomalous transport is quite universal and almost completely independent of the parameters of the model (Coulomb interaction and chemical potential): It is mainly determined by the initial distribution of particles along the chain. We corroborate our findings by analytical arguments: scaling analysis for the anomalous regime and the Langevin equationfor the normal diffusion regime.

Edge effects of a fragmented seagrass habitat on flow, bivalve recruitment, and sediment dynamics

In both continuous and fragmented seagrass ecosystems, the vegetation edge can be a location of abrupt hydrodynamic change, with impacts to both ecological and physical processes. We address how flow and wave activity change across seagrass meadow edges and the effects of vegetation on sediment dynamics and bivalve recruitment. Two Zostera marina seagrass meadow sites were monitored: a high-density site with >500 shoots m-2 and a low-density site with <250 shoots m-2. Mean flow velocities were significantly reduced in seagrass vegetation adjacent to edges, with reductions compared to unvegetated areas ranging from 30-75%. Recruitment of juvenile bivalves was significantly elevated within vegetation. No significant differences in wave activity or sediment suspension and/or deposition were found spatially across a 10 m distance from a seagrass edge, but significant temporal variability was observed, caused by periodic storms. Wave height was a major predictor for sediment movement along seagrass edges, with an observed 10-fold increase in sediment collection within benthic traps following severe storms. These results were found across various heterogeneous edge configurations and reveal abrupt hydrodynamic responses of both mean flow and turbulence to occur at short spatial scales (1-10 m), with changes to wave and sediment deposition and/or suspension conditions only occurring over larger spatial distances (~100 m). Changes to the hydrodynamic regime were therefore found to be driven by meteorological conditions (e.g. winds, storms) on daily timescales and by changes in seagrass shoot density, altering both bivalve recruitment and sediment dynamics on longer temporal and/or spatial timescales.

A potential solution for suspended solids accumulation on a tidally inundated stormwater canal in Valparaiso Bay, Chile

Low-relief coastal cities have experienced increased flooding due to climate change. During high tides or swell surges, stormwater canals or pipes can be inundated by coastal waters, causing suspended solids (SS) to accumulate at the conduits’ outfall. The City of Valparaiso (Chile) is currently upgrading its stormwater network with costly underground stormwater aqueducts such as the coastal “Argentina stormwater underground canal” (ASC). However, soon after the ASC was put in operation, sea water intrusion and bidirectional flow at the lowest sectors of the canal decreased its water conveying capacity, and SS (that otherwise would have been carried to Valparaiso Bay) accumulated in the lower sectors of the canal, close to its outfall. Urban growth and reduction of pervious land covers could worsen the current situation. Therefore, the current ASC outfall seems to be an unsustainable solution to conveyance of rainwater and SS. In this research, a hydrodynamic model of Valparaiso Bay and the ASC is presented. The current ASC hydrodynamic regime is described. The validated hydrodynamic model is used to explore the feasibility of using a submarine outfall to transport the accumulated muddy water to an offshore location. The effects of sea level rise on the existing stormwater canal are studied, and its potential to further prevent an efficient conveyance of rainwater from the city to Valparaiso Bay is explored.

Tailoring microstructures of oleogel-based HIPEs to modulate oral processing properties: Rheology, tribology and mastication effects

High internal phase emulsions (HIPEs, 80 wt%) with different structures were developed by using different oleogelators (beeswax and ethyl cellulose) and emulsifiers (whey protein isolate and OSA starch) via a facile shearing approach. The effects of the oleogelators and emulsifiers on the stability and oral processing properties were investigated. The addition of oleogelator resulted in smaller particle sizes and higher accelerated centrifugal stability. Microstructural observations indicated the droplets were tightly packed to form oil-in-water HIPEs. Rheology tests showed that the addition of the oleogelators resulted in strain-thinning behavior and weak strain overshoot for OSA and WPI stabilized HIPEs, respectively. Tribology tests suggested that emulsifiers dominated the lubrication properties of the mixing regime, whereas oleogelators were crucial to the lubricating effects of the hydrodynamic regime. Instrumental mastication assays revealed that the WPI-HIPEs required stronger chewing force, and the addition of oleogelator weakened the normal force. After being masticated by the bionic chewing robot, droplet coalescence and phase separation occurred in the HIPEs, which was attenuated by the addition of oleogelators. These findings will assist in designing the structures of desirable textural attributes and support the creation of functional foods.

Hydrodynamic Modeling of Water Renewal Time and Potential Dissolved Matter Using TELEMAC: Applications to Shediac Bay (New Brunswick, Canada)

This study examines the hydrodynamic regimes in Shediac Bay, located in New Brunswick, Canada, with a focus on the breach in the Grande-Digue sand spit. The breach, which was developed in the mid-1980s, has raised concerns about its potential impacts on water renewal time and water quality in the inner bay. The aims of this study, using mathematical modeling approaches, were to evaluate the flow regimes passing through the breach and influences on the distribution of dissolved matter, providing insights into whether the breach should be allowed to naturally evolve or be artificially infilled to prevent contaminant stagnancy in the bay. The study considered three simulation scenarios to comprehend the water renewal time and the role of the breach in the environmental management of Shediac Bay. Results indicated that completely closing the breach would significantly increase the water renewal time in the inner bay, although the spatial extent of this increase is limited. However, the study identified some limitations, including the need to better define the concentration limit for considering water as renewed and the lack of consideration of dynamic factors such as wind and wave effects.

Gas-kinetic scheme for partially ionized plasma in hydrodynamic regime

Most plasmas are only partially ionized. To better understand the dynamics of these plasmas, the behaviors of a mixture of neutral species and plasma in ideal magnetohydrodynamic states are investigated. The current approach is about the construction of coupled kinetic models for the neutral gas, electron, and proton, and the development of the corresponding gas-kinetic scheme (GKS) for the solution in the continuum flow regime. The scheme is validated in the 1D Riemann problem for an enlarged system with the interaction from the Euler waves of the neutral gas and magnetohydrodynamic ones of the plasma. Additionally, the Orszag–Tang vortex problem across different ionized states is tested to examine the influence of neutrals on the MHD wave evolution. These tests demonstrate that the proposed scheme can capture the fundamental features of ideal partially ionized plasma, and a transition in the wave structure from the ideal MHD solution of the fully ionized plasma to the Euler solution of the neutral gas is obtained.

Variable downcanyon morphology controlling the recent activity of shelf-incised submarine canyons (Alboran Sea, western Mediterranean)

This research aims to distinguish genetic sedimentary processes building canyon geomorphological patterns and the factors driving different sedimentary activities in two nearby Mediterranean shelf-incised submarine canyons (Carchuna and Motril) that exhibit different degrees of incision on the narrow margin of the northern Alboran Sea.The straight Carchuna Canyon incises the shelf up to 200 m off the coastline and exhibit steep canyon walls featuring narrow terraces, muddy sands with high contents of organic matter along the thalweg, and transported shelf benthic foraminifera in distal settings. The Motril Canyon head is wider and incises the shelf edge, ca. 2 km off the coastline. It exhibits a sinuous morphology and less steep walls, wider terraces, and higher sedimentation rates with muddy sediments along the thalweg. In both canyons, cross-section relief, width, incision, and area decrease downslope, although these parameters increase locally.The downslope variations of geomorphological parameters are attributed to enhanced erosional/depositional processes promoted by tectonically controlled abrupt changes of the axial channel orientation. The degree of shelf incision, the location of the canyon heads in relation with the local sediment sources, and the seasonally variable hydrodynamic regimes determine the different degrees of recent canyon activity. The Motril Canyon is interpreted as a mature system that reflects episodic activity, collecting fine-grained sediments from the nearby Guadalfeo River. The Carchuna Canyon exhibits a youthful developmental stage whose activity is more continuous and involves sediment trapping of littoral cells and continuous downslope sand transport.

Collective excitations of a Bose-condensed gas: Fate of second sound in the crossover regime between hydrodynamic and collisionless regimes

Collective excitations of a Bose-condensed gas: Fate of second sound in the crossover regime between hydrodynamic and collisionless regimes

Effects of hydropeaking by an upstream dam on thermal mixing in a riverine lake

The hydropeaking operations of a hydropower dam can significantly affect the flow and thermal regimes in riverine reservoirs, and this effect is very complex, both in space and time. In this study, we used a 3D hydrodynamic model, calibrated with field datasets, to investigate the thermal mixing resulting from hydropeaking within Paldang Lake (PL) in South Korea. The spatiotemporal temperature patterns revealed that density currents critically affected thermal mixing in the reservoir and developed differently based on upstream dam operations and flooding events. Notably, the confluence of the North Han River (NHR) and South Han River (SHR) played a key role in shaping the thermal regime. During the hydropeaking release from the upstream dam in the NHR, the colder water of the NHR from the deep-water discharge of the upstream dam plunged beneath the warmer water of the SHR, leading to three-dimensional mixing. Consequently, the thermal mixing patterns varied depending on the discharge patterns from the upstream dam. Additionally, diurnal variations in the dam discharge frequently affected areas of the reservoir exhibiting high Schmidt stability. During the non-operation period of the upstream dam, the SHR flow backflowed into the downstream section of the NHR, resulting in the confluent area exhibiting the poorest vertical mixing. Secondary currents also played a crucial role in influencing the flow and thermal regimes, with the intensity of the secondary flow varying along the longitudinal mainstream of the reservoir. The thermal mixing state was predominantly weakened to partial mixing within a curved reach owing to the secondary current. Overall, this study demonstrates that the complexity of flow and thermal processes in the PL is significantly influenced by hydropeaking events. These findings emphasize the importance of understanding density currents and secondary flows according to dam operation in managing riverine reservoirs for enhanced ecological health and sustainable water resource management.